- published: 22 Nov 2011
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In astronomy, Kepler's laws of planetary motion are three scientific laws describing the motion of planets around the Sun.
Most planetary orbits are almost circles, and careful observation and calculation is required in order to establish that they are actually ellipses. Using calculations of the orbit of Mars, whose published values are somewhat suspect, which indicated elliptical orbits, Johannes Kepler inferred that other heavenly bodies, including those farther away from the Sun, also have elliptical orbits.
Kepler's work (published between 1609 and 1619) improved the heliocentric theory of Nicolaus Copernicus, explaining how the planets' speeds varied, and using elliptical orbits rather than circular orbits with epicycles.